Short answer up top: a supernova remnant is what's left after a massive star explodes — an expanding shell of shocked gas and dust that keeps glowing, faintly, for tens of thousands of years after the star itself is gone. NASA's Astronomy Picture of the Day for September 24, 2026, "The Ghosts of Five Supernovas," is a rare case of seeing five of them in a single frame: a deep mosaic by photographers Stephane Vetter and Yann Sainty, taken from the Oukaïmeden Observatory in Morocco, covering an area of sky equivalent to one thousand full moons tiled together — all within the constellation Auriga, the Charioteer.
What's actually in this picture?
Five separate supernova remnants sit scattered across the frame, cataloged as G181.1+9.5, G182.4+4.3, G179.0+2.6, G180.0−1.7, and G178.2−4.2. The fourth one has a name most skywatchers will recognize even without the catalog number: it's Sh2-240, better known as the Spaghetti Nebula, for the tangled, noodle-like filaments visible in close-up images of it. The mosaic doesn't stop at supernova remnants, either — it also catches the open star cluster M37 and the Tadpole Nebula sharing the same stretch of sky, all of it estimated to lie up to several thousand light-years from Earth.
Why does an exploded star leave "ghosts" behind?
The name fits better than it might first sound. When a massive star runs out of fuel and detonates as a supernova, the explosion doesn't just vanish once the initial flash fades — it drives a shockwave outward into the surrounding interstellar gas, sweeping it into thin, glowing filaments as it goes. NASA describes exactly that structure here: shocked gas traced in red light from hydrogen and blue light from oxygen, arranged in delicate filamentary patterns across all five remnants. The star that caused each explosion is long gone. What remains is this slowly fading shell, still visibly expanding, still glowing from an event that ended visually within weeks or months of the original blast — which is genuinely how it would have looked to anyone watching from Earth without a telescope: a new star flaring up bright, then fading away, as NASA notes early skywatchers may well have witnessed.
Why did this image take 200 hours to make?
Supernova remnants like these are old and faint — this is light from gas that's been cooling and dimming for tens of thousands of years, spread thin across an enormous area of sky. Catching five of them clearly, in the same frame, at a scale of a thousand full moons, isn't something a single exposure can do. It took roughly 200 hours of accumulated observation time to gather enough faint red and blue light to bring out the filamentary detail NASA highlights in this release — a reminder that some of the most striking deep-sky images aren't single snapshots at all, but the sum of many, many nights of patient data collection.
Putting "several thousand light-years" in perspective
Solar System Live's real-time 3D simulator doesn't track supernova remnants — it's built around the Sun, the planets, and their moons, all of which sit within light-hours of each other, not light-years. But that's exactly what makes it a useful contrast here. Open the simulator and look at how long sunlight takes to cross our own solar system: minutes to Earth, a few hours out to Neptune. Now hold that against the light captured in this image, which left these five stellar explosions thousands of years before it reached a camera in Morocco. The comparison won't make the Spaghetti Nebula and its neighbors any closer, but it puts a real number behind just how vast the gap is between "our solar system" and "everything else."